Termites are well known throughout most areas of the world. These insects that attack and destroy wooden structures are classified into four principal categories, i.e., subterranean, formosan, damp wood, and dry wood. The invention is particularly directed to poisoning of subterranean, damp wood, and formosan termites. (Dry wood termites live in wood with relatively small moisture content in particular areas of the world and are not present in the soil.) Many methods for killing termites have been practiced over the years. Frequently, some termite-killing chemical is applied to the soil in the vicinity of a structure that is to be protected from termites. Many of the termiticides that have been used have lasted in the soil for a long time and do not break down into innocuous residues. An example of such a long-lasting chemical that has been used for many years is chlordane. However, chlordane and other halogenated insecticides, such as DDT, aldrin, dieldrin, and heptachlor have harmful effects. The residues of these chlorinated insecticides remain in the soil for very long periods of time and it is known or believed that some of these insecticides are dangerous to humans and higher life forms including other mammals. Because of these environmental hazards, use of many of these insecticides has been severely limited or prohibited. Typically, these insecticides are applied directly to the soil near a structure to be protected, forming a subterranean "curtain" or barrier that kills termites that attempt to pass through the barrier. These insecticides not only are hazardous because of their long lifetime and the nature of the residues they leave but are also hazardous to the persons involved in the manufacture and application of the insecticides to the soil.
As a substitute for introducing a "curtain" of an insecticide into the soil adjacent a structure to be protected against termite infestation, sometimes structures are built of wood that has been pressure-treated to retard termite infestation. Generally, the pressure-treated wood is not impregnated with the treating material through its entire thickness so that termites and rot invade the parts of that pressure-treated wood that has not been impregnated with the protecting material. Many of the materials used for those wood treatments are themselves dangerous, both in application, as are the insecticides, and in use through the risk of leaching or other escape of the toxic materials. For example, the material with which the wood is treated has a finite vapor pressure at normal temperatures so that some of the material can escape slowly over time into a structure. Pressure-treated wood that is commonly sold as lasting for a long period of time, even in direct contact with soil, may contain arsenic, heavy metals, or other toxic elements that can undesirably escape into the ambient or leach into contacting fluids or soil, leaving potentially toxic residues.